System and method for discriminating radar transmissions from wireless network transmissions and wireless network having radar-avoidance capability

ABSTRACT

For use in a wireless network, systems and methods for identifying radar signals and for giving the wireless network a radar-avoidance capability. The system for identifying radar signals includes: (1) a pulse analyzer, associated with a wireless device, configured to make a determination whether a received pulse is a radar pulse and not a wireless network pulse and (2) a pulse reporter configured to generate, if the determination is positive, a report thereof for transmission over the wireless network. Another system gives the wireless network a radar-avoidance capability and includes: (1) a report receiver configured to receive reports via the wireless network from wireless devices thereof and (2) a report analyzer, associated with the report receiver, configured to analyze relationships among the reports to make a determination whether a sequence of radar pulses exists and, if the determination is positive, generate a radar transmission alert.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to wireless networkingand, more specifically, to a system and method for discriminating radartransmissions from wireless network transmissions and wireless networkhaving radar-avoidance capability.

BACKGROUND OF THE INVENTION

One of the fastest growing technologies over the last few years has beenwireless local area network (WLAN) devices based on the Institute ofElectrical and Electronic Engineers (IEEE) 802.11b standard, commonlyknown as “Wi-Fi.” The 802.11b standard uses the 2.4 GHz frequency of theelectromagnetic spectrum and allows users to transfer data at speeds upto 11 Mbit/sec.

However, a complementary WLAN standard (IEEE 802.11a) is now availablethat specifies how WLAN equipment has to operate on frequencies between5 GHz and 6 GHz (the “5 GHz band”). The 802.11a standard significantlyexpands the capacity of WLANs, allowing data to be exchanged at evenfaster rates (up to 54 Mbit/sec), but at a shorter operating range than802.11b.

Unfortunately, the Department of Defense (DOD) operates a large numberof radar systems in the 5 GHz band. The DOD has become concerned thatthe increasing adoption of 802.11a wireless devices will, as time goeson, cause increasing interference between the pulses that make up thesignals produced by the radar systems and the pulses produced by thewireless devices. Its concern is particularly acute in today'ssecurity-conscious environment.

To accommodate both radar and 802.11a WLAN wireless devices in the same5 GHz band, the WLAN industry developed a concept called “dynamicfrequency selection,” or DFS. DFS calls for wireless devices to detectthe presence of radar signals. When a radar signal is detected on aparticular channel, the wireless devices are to switch automatically toanother channel to avoid interfering with the radar signal. DFS wouldappear in theory to yield an acceptable sharing of the 5 GHz band.

However, several problems have arisen in prior art implementations ofDFS. First, switching sensitivity is a serious issue. If a particularimplementation of DFS provides good noise rejection, switching may occurtoo slowly in response to a real radar transmission, resulting in undueinterference. However, if the noise rejection is reduced, switching mayoccur in response to noise that appears to be a real radar transmission.The resulting needless channel switch reduces the efficiency with whichuser data is transmitted through the WLAN, and therefore reduces itseffective bandwidth.

Second, DFS can only be undertaken in a wireless device when it isreceiving, not when it is transmitting, since its receiver iseffectively disabled during that time. Therefore, radar signals willalmost certainly go undetected when the wireless device is transmitting,increasing the risk of unwanted interference to radar systems.

Fourth, some radar systems transmit the pulses of their radar signals ata low rate. If a wireless device misses detecting even one pulse, thetime interval between the two adjacent pulses may be too great for thewireless device properly to identify the radar transmissions. Again, theradar transmissions may go undetected.

Finally, the position of the 802.11a wireless device with respect to theradar may be such that radar transmissions received by the wirelessdevice are of enhanced or diminished amplitude. The transmissions maytherefore be misinterpreted as noise and ignored. In a similar vein,multipath interference may transform the pulses of the radartransmission, rendering them unrecognizable as such by the 802.11awireless device. Again, the extent to which noise is rejected has somebearing on noninterpretation or misinterpretation of radartransmissions. In either case, the risk is that channels would not beswitched quickly enough, and interference results.

While the IEEE does, in 802.11h, provide a protocol that allowsradar-monitoring data to be collected from wireless devices, it setsforth no method for actually monitoring radar transmissions, nor does itspecify how the radar-monitoring data should be analyzed to determinewhether a radar is in operation. What is needed in the art is acomprehensive, practical DFS implementation that effectively rejectsnoise, but quickly and correctly identifies true radar transmissions.What is further needed in the art is a DFS implementation that isoperable even when a particular wireless device is transmitting.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides for use in a wireless network (of which aWLAN is one type), systems and methods for identifying radar signals andfor giving the wireless network a radar-avoidance capability.

In one embodiment, the system for identifying radar signals includes apulse analyzer, associated with a wireless device, configured to make adetermination whether a received pulse is a radar pulse and not awireless network pulse. The system further includes a pulse reporterconfigured to generate, if the determination is positive, a reportthereof for transmission over the wireless network.

In one embodiment, the method of identifying radar signals includesmaking, at a wireless device in the wireless network, a determinationwhether a received pulse is a radar pulse and not a wireless networkpulse. The method further includes generating, if the determination ispositive, a report thereof for transmission over the wireless network.

In one embodiment, the system for giving the wireless network aradar-avoidance capability includes a report receiver configured toreceive reports via the wireless network from wireless devices thereof.The system further includes a report analyzer, associated with thereport receiver, configured to analyze relationships among the reportsto make a determination whether a sequence of radar pulses exists and,if the determination is positive, generate a radar transmission alert.

Therefore, the present invention introduces the broad concept ofemploying the wireless network as a whole (or at least a number of itswireless devices) to gather radar pulse data and using a node in thewireless network to analyze the data centrally. Using multiple wirelessdevices overcomes the many problems described above (e.g., transmitblackout, multipath interference, noise and amplitude variation) thatresult when only one wireless device is used. Once it has beendetermined that radar transmissions are present on the wirelessnetwork's frequency, the wireless network responds by changing frequencyto avoid the radar.

The foregoing has outlined, rather broadly, preferred and alternativefeatures of the present invention so that those skilled in the art maybetter understand the detailed description of the invention thatfollows. Additional features of the invention will be describedhereinafter that form the subject of the claims of the invention. Thoseskilled in the art should appreciate that they can readily use thedisclosed conception and specific embodiment as a basis for designing ormodifying other structures for carrying out the same purposes of thepresent invention. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention in its broadest form.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a schematic diagram of a WLAN operating in anenvironment in which a radar system is also operating;

FIG. 2 illustrates a block diagram of one embodiment of a system foridentifying radar signals constructed according to the principles of thepresent invention;

FIG. 3 illustrates a flow diagram of one embodiment of a method ofidentifying radar signals carried out according to the principles of thepresent invention;

FIG. 4 illustrates a block diagram of one embodiment of a system forgiving the WLAN of FIG. 1 a radar-avoidance capability constructedaccording to the principles of the present invention;

FIG. 5A through 5E illustrate exemplary graphical representations ofpulses that the system of FIG. 4 can analyze to identify radar pulsesequences; and

FIG. 6 illustrates a flow diagram of one embodiment of a method ofgiving the WLAN of FIG. 1 a radar-avoidance capability carried outaccording to the principles of the present invention.

DETAILED DESCRIPTION

Referring initially to FIG. 1, illustrated is a schematic diagram of aWLAN, generally designated 100, operating in an environment in which aradar system 110 is also operating. The WLAN 100 includes a plurality ofwireless devices 120, 130, 140, 150, 160, 170. The WLAN 100 is furtherillustrated as including a Wireless Access Point (WAP) 180 that providesa bridge between the various wireless devices 120, 130, 140, 150, 160,160 of the WLAN 100 and an external network (not shown), such as theInternet. Finally, a reflective surface 190 is schematically shown for apurpose that will soon become evident.

During operation of the WLAN 100, the wireless devices 120, 130, 140,150, 160, 170 transmit and receive packets of user and control data.Since the wireless devices 120, 130, 140, 150, 160, 170 conform to theIEEE 802.11a standard, the packets are transmitted between the wirelessdevices 120, 130, 140, 150, 160, 170 and the WAP 180 using codedOrthogonal Frequency Division Multiplexing (OFDM) symbols that take theform of pulses that, in turn, modulate a carrier wave of a certainfrequency. The frequency of the carrier wave defines the channel atwhich the wireless devices 120, 130, 140, 150, 160, 170 are operating.

From the perspective of the Open Systems Interconnect (OSI) networkmodel, the OFDM symbols are coded, transmitted, received and decoded atthe physical, or “PHY,” layer. All other data manipulation occurs athigher layers.

For purposes of illustration, it is now assumed that the radar system110 begins to transmit at a frequency that approximates the frequency ofthe channel at which the WLAN 100 is operating. Radar pulses emanatefrom the radar system 110 and begin to traverse the WLAN's space. Theresult, as amply described in the Background of the Invention sectionabove, is that the continued operation of the WLAN 100 on its currentchannel begins to interfere with the receiver of the radar system 110.

The challenge at this point for the WLAN 100 is to detect and correctlyidentify the radar pulses and switch channels to halt furtherinterference. Each of the wireless devices 120, 130, 140, 150, 160, 170could try to detect and identify the radar pulses independently but, asdescribed above, significant barriers exist to this approach.

To illustrate by way of example, the wireless device 170 is relativelyclose to the radar system 110. Radar pulses may appear enhanced inamplitude or distorted by virtue of their relative power. In contrast,the wireless device 160 is relatively far from the radar system 110.Radar pulses may appear diminished in amplitude and be subject to beingtreated as noise. Still further in contrast, the wireless device 130 isproximate the reflective surface 190. Not only does the wireless device130 receive radar pulses directly from the radar system 110, it alsoreceives delayed, attenuated and probably distorted reflections of theradar pulses by virtue of their interaction with the reflective surface190. It would be quite difficult to provide a common set of knowncharacteristics (e.g., time interval, pulsewidth or amplitude) to thewireless devices 120, 130, 140, 150, 160, 170 that would allow them eachreliably to distinguish numbers of radar pulses from wireless networkpulses sufficient to reach a reliable determination, since theirperceptions of the radar pulses differ.

Compounding the challenge is that the wireless devices 120, 130, 140,150, 160, 170 are unable to detect radar pulses while they aretransmitting, so the wireless devices 170, 160, 130 cannot be assumed tohave complete data from which to make their respective determinations.

As stated above, the present invention takes a different approach,calling for the various wireless devices 120, 130, 140, 150, 160, 170 toidentify as many radar pulses as reasonably possible given theircircumstances and to pool their findings such that a more comprehensiveanalysis can be performed centrally on a larger body of collective data.Embodiments of the present invention will now be described to describethis process in greater detail.

Turning now to FIG. 2, illustrated is a block diagram of one embodimentof a system, generally designated 200, for identifying radar signalsconstructed according to the principles of the present invention. Theillustrated embodiment of the system 200 embodied in each of thewireless devices 120, 130, 140, 150, 160, 170. As such, the system 200has access to and employs a receiver 210, a digital signal processor(DSP) 220 and a media access controller (MAC) 230 already existing ineach of the wireless devices 120, 130, 140, 150, 160, 170. Those skilledin the pertinent art understand that, as conventional OFDM symbols arereceived into a particular wireless device, its receiver amplifies,demodulates and filters the received symbols; its DSP decodes thesymbols to yield a bitstream; and its MAC applies protocols to andbuffers the bitstream so it can be transferred to the remainder of thewireless device.

The system 200 includes a pulse analyzer 240. The pulse analyzer 240 isconfigured to make a determination whether a received pulse is a radarpulse and not a wireless network pulse. As such, the pulse analyzer 240compares the received pulse to at least one known characteristic. In theillustrated embodiment, the pulse analyzer 240 is embodied as a sequenceof instructions executable in the DSP 220 and employs programmablecharacteristics that distinguish the radar pulse, the wireless networkpulse and noise from one another.

If the pulse analyzer 240 determines that the received pulse is noise,it causes the received pulse to be filtered out. If the pulse analyzer240 determines that the received pulse is a wireless network pulse, itcauses the received pulse to be decoded in the DSP 220 and passed on tothe MAC 230 for standard processing. If the pulse analyzer 240 makes adetermination that the received pulse is a radar pulse, it signals apulse reporter 250.

The pulse reporter 250 is coupled to the pulse analyzer 240 and isconfigured to generate, if the determination is positive, a reportthereof for transmission over the WLAN (100 of FIG. 1). More specific tothe illustrated embodiment, the pulse reporter 250 is embodied in theMAC 230, allowing it to generate a packet of proper protocol containingthe report. One such a packet may contain one or more of these reports.

The report includes at least a timestamp derived from a common timebase.The fact that the MAC 230 already has a real time clock synchronizedwith other real time clocks in the WLAN (100 of FIG. 1) advantageouslyallows it to provide the timestamp. In the illustrated embodiment, thetimestamp indicates the onset (arrival) time of the pulse. The report ofthe illustrated embodiment further includes a pulsewidth which may proveuseful in later analysis. The report can also include pulse amplitude,frequency, phase or any other characteristic that may be deemed usefulin a particular implementation of the present invention.

Accordingly, the MAC 230, under control of the pulse reporter 250,generates the report and causes the report to be destined for a “centralaggregation node” in the WLAN (100 of FIG. 1). A number of these reportsmay be combined and transmitted in one transmission. In the illustratedembodiment, the central aggregation node is the WAP 180 of FIG. 1. Thoseskilled in the art will readily realize, however, that this need not bethe case.

Turning now to FIG. 3, illustrated is a flow diagram of one embodimentof a method, generally designated 300, of identifying radar signalscarried out according to the principles of the present invention. Themethod 300 begins in a start step 310, wherein it is desired to monitorpulses to determine whether they may indicate the presence of a radarsystem on the channel being used.

The method proceeds to a determination of whether a received pulse is aradar pulse and not a wireless network pulse (and perhaps not noiseeither). Accordingly, in a step 320, the received pulse is compared toat least one known characteristic (e.g., time interval, pulsewidth oramplitude). In the illustrated embodiment, time interval and pulsewidthare the employed characteristics and are programmable such that thesensitivity of the WLAN (100 of FIG. 1) can be altered. If the receivedpulse is determined to be noise, the received pulse is filtered out in astep 330.

Next, in a step 340, if the determination that the received pulse is aradar pulse and not a wireless network pulse is positive, a report ofthat fact is generated for transmission over the WLAN (100 of FIG. 1).In the illustrated embodiment, the report is sent to the WAP (180 ofFIG. 1), which serves as a central aggregation node for reports from allwireless devices of the WLAN (100 of FIG. 1). Those skilled in thepertinent art will recognize that the report sent to the WAP (180 ofFIG. 1) may be aggregated with other reports into a single message overthe WLAN (100 of FIG. 1). At this point, it is assumed that monitoringof received pulses continues, subject to periods during which thewireless device is transmitting data. Accordingly, the method 300doubles back to the step 310.

Turning back briefly to FIG. 1, it should be assumed at this point that,given that the radar system 110 of FIG. 1 is active on their channel,the various wireless devices 120, 130, 140, 150, 160, 170 aretransmitting various reports to the WAP 180 concerning suspected radarpulses they have received therefrom. The term “suspected” is used,because the wireless devices 120, 130, 140, 150, 160, 170 may haveincorrectly determined some noise to be radar pulses and caused spuriousreports to have been transmitted. Nonetheless, such spurious reportswill be dealt with in a manner that will become apparent.

Turning now to FIG. 4, illustrated is a block diagram of one embodimentof a system, generally designated 400, for giving the WLAN of FIG. 1 aradar-avoidance capability constructed according to the principles ofthe present invention. The illustrated embodiment of the system 400 isembodied as a sequence of software instructions executable in a generalpurpose processor associated with the WAP 180. Those skilled in thepertinent art will understand that other embodiments and locations forthe system 400 fall within the broad scope of the present invention.

The system 400 includes a report receiver 410. The report receiver 410is configured to receive reports of received radar pulses via the WLAN(100 of FIG. 1) from wireless devices thereof, (e.g., the wirelessdevices 120, 130, 140, 150, 160, 170). The illustrated embodiment of thereport receiver 410 assembles the data contained in the reports into atable (not shown, but represented schematically in FIGS. 5A through 5E)in timestamp order to facilitate analysis.

The system 400 further includes a report analyzer 420. The reportanalyzer 420 is associated with the report receiver 410 and isconfigured to analyze relationships among the reports to make adetermination whether a sequence of radar pulses exists. If thedetermination is positive, the report analyzer 420 generates a radartransmission alert to be employed by the WLAN (100 of FIG. 1) inswitching channels to avoid the radar system (110 of FIG. 1). Uponreceiving the radar transmission alert, the WLAN (100 of FIG. 1)responds by ordering a channel switch, and the wireless devices (e.g.,the wireless devices 120, 130, 140, 150, 160, 170 of FIG. 1) respond toeffect the switch.

As described above, the reports of the illustrated embodiment includetimestamps derived from a common timebase and widths of the radar pulses(pulsewidths). Accordingly, the illustrated embodiment of the reportanalyzer 420 analyzes time intervals between ones of the radar pulsesand further analyzes the pulsewidths.

More specifically, the report analyzer identifies X successiverepetitions of a given time interval between ones of the radar pulsessubject to a maximum of Y missing radar pulses and within a tolerance ofZ microseconds, where X, Y and Z are programmable variables provided tothe system 400. Thus X, Y and Z together determine the sensitivity ofthe system 400. Those skilled in the pertinent art will understand thatother or further variables may be employed to advantage to identifyradar signals.

Moreover, the report analyzer 420 identifies a maximum of N timeintervals between ones of the radar pulses, where N is a programmablevariable. N thus determines how thorough the search for like timeintervals is to be before calling the search off and beginning to searchfor wholly different time intervals.

Some details regarding the analysis of specific radar pulses will now beillustrated. FIG. 5A through 5E illustrate exemplary graphicalrepresentations of pulses that the system 400 of FIG. 4 can analyze toidentify radar pulse sequences.

FIG. 5A illustrates six pulses 510 a, 510 b, 510 c, 510 d, 510 e, 510 fof substantially constant width and periodicity, but with somevariation. (Keep in mind that these pulses 510 a, 510 b, 510 c, 510 d,510 e, 510 f may have been collected from various and even multiplewireless devices.) As FIG. 5A indicates, the interval between pulses 510a and 510 b is 200 μsec. The interval between pulses 510 b and 510 c is210 μsec. The interval between pulses 510 c and 510 d is 190 μsec. Theinterval between pulses 510 d and 510 e is 205 μsec. Finally, theinterval between pulses 510 e and 510 f is 198 μsec. If the given timeinterval is 200 μsec and the tolerance Z is 10 μsec, the report analyzer420 will regard the six pulses 510 a, 510 b, 510 c, 510 d, 510 e, 510 fas belonging to a sequence of radar pulses. The report analyzer 420 maynot regard the sequence as complete, however, if X, the number ofsuccessive repetitions of a given time interval required to constitute avalid radar pulse sequence, is greater than six.

FIG. 5B illustrates three pulses 520 a, 520 b, 520 c separated byarguably similar time intervals. However, the pulse 520 b is quiteevidently wider than the pulses 520 a, 520 c. In the illustratedembodiment, the pulse 520 b would be disregarded as noise. Aprogrammable variable W may achieve the purpose of defining the maximumwidth variation tolerance.

FIG. 5C illustrates seven pulses 530 a, 530 b, 530 c, 530 d, 530 e, 530f, 530 g. The pulse 530 c stands out from the rest as being the only oneof its amplitude. In the illustrated embodiment, the pulse 530 c wouldbe disregarded as noise. A programmable variable A may achieve thepurpose of defining the maximum amplitude variation tolerance.

FIG. 5D illustrates nine pulses 540 a, 540 b, 540 c, 540 d, 540 e, 540f, 540 g, 540 h, 540 i. It is apparent that the pulses 540 a, 540 d, 540h potentially belong (subject to X, Y and Z) to a first sequence ofradar pulses (emanating from what appears to be a first radar system)and the remainder of the pulses 540 b, 540 c, 540 e, 540 f, 540 g, 540 ipotentially belong (subject again to X, Y and Z) to a second sequence ofradar pulses (emanating from what appears to be a second radar system).FIG. 5D illustrates the ability of the report analyzer 420 to discernmultiple radar pulse sequences, subject to N.

FIG. 5E illustrates the consequence of Y. Five pulses 550 a, 550 b, 550c, 550 d, 550 e are evident, but the time interval separating the pulses550 b and 550 c appears to be twice those separating the others.Assuming that Y is set to at least one, the double time interval will beassumed to be missing a pulse, and the five pulses 550 a, 550 b, 550 c,550 d, 550 e actually in evidence will be candidates (subject to X andZ) for a potential sequence of radar pulses.

Turning now to FIG. 6, illustrated is a flow diagram of one embodimentof a method, generally designated 600, of giving the WLAN 100 of FIG. 1a radar-avoidance capability carried out according to the principles ofthe present invention. The method 600 begins in a start step 610,wherein it is desired to collect up and centrally analyze pulses in aneffort to detect radar signals.

The method 600 proceeds to a step 620, in which data pertaining topulses determined by various wireless devices to be radar pulses arecollected into a table and pulses that are apparent duplicates (the samepulse determined by multiple wireless devices) are discarded. Next, in astep 630, the first time interval in the table is measured.

Then, in a step 640, the table is scanned to find a sequence of at leastX successive repetitions of the time interval. A sequence is stillconsidered to be valid even if Y pulses are missing. When comparing timeintervals, a tolerance of Z μsec is allowed.

Next, in a decisional step 650, it is determined whether a sequence hasbeen found in the table. If YES, then the method 600 ends in an end step690. If NO, the method 600 proceeds to a decisional step 660 in which itis determined whether N such time intervals have been found. If YES, thesearch for like time intervals ceases, and the next time interval in thetable is measured in a step 670. Processing then continues in the step640. If NO, the method proceeds to a step 680 in which the time intervalin the table is incremented. Processing then continues in the step 640.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

1. For use in a wireless network, a system for identifying radarsignals, comprising: a pulse analyzer, associated with a wireless devicein said wireless network, configured to make a determination whether areceived pulse is a radar pulse and not a wireless network pulse; and apulse reporter, coupled to said pulse analyzer, configured to generate,if said determination is positive, a report thereof for transmissionover said wireless network.
 2. The system as recited in claim 1 whereinsaid pulse analyzer filters out said received pulse if said pulseanalyzer determines that said received pulse is noise.
 3. The system asrecited in claim 1 wherein said pulse analyzer makes said determinationby comparing said received pulse to a known characteristic.
 4. Thesystem as recited in claim 1 wherein said pulse analyzer is embodied ina digital signal processor and employs programmable characteristics thatdistinguish said radar pulse, said wireless network pulse and noise. 5.The system as recited in claim 1 wherein said pulse reporter is embodiedin a MAC and said report includes a timestamp derived from a commontimebase.
 6. The system as recited in claim 1 wherein said report isdestined for a central aggregation node in said wireless network.
 7. Thesystem as recited in claim 1 wherein said wireless network pulse is anOFDM pulse conforming to IEEE 802.11a and said radar pulse is in a 5 GHzband.
 8. For use in a wireless network, a method of identifying radarsignals, comprising: making, at a wireless device in said wirelessnetwork, a determination whether a received pulse is a radar pulse andnot a wireless network pulse; and generating, if said determination ispositive, a report thereof for transmission over said wireless network.9. The method as recited in claim 8 further comprising filtering outsaid received pulse if said received pulse is determined to be noise.10. The method as recited in claim 8 wherein said making comprisesmaking said determination by comparing said received pulse to a knowncharacteristic.
 11. The method as recited in claim 8 wherein said makingis carried out in a digital signal processor and comprises employingprogrammable characteristics that distinguish said radar pulse, saidwireless network pulse and noise.
 12. The method as recited in claim 8wherein said generating is carried out in a MAC and said report includesa timestamp derived from a common timebase.
 13. The method as recited inclaim 8 further comprising sending said report to a central aggregationnode in said wireless network.
 14. The method as recited in claim 8wherein said wireless network pulse is an OFDM pulse conforming to IEEE802.11a and said radar pulse is in a 5 GHz band.
 15. A system for givingsaid wireless network a radar-avoidance capability, comprising: a reportreceiver configured to receive reports of received radar pulses via saidwireless network from wireless devices thereof; and a report analyzer,associated with said report receiver, configured to analyzerelationships among said reports to make a determination whether asequence of radar pulses exists and, if said determination is positive,generate a radar transmission alert.
 16. The system as recited in claim15 wherein said reports includes timestamps derived from a commontimebase and said report analyzer analyzes time intervals between onesof said radar pulses.
 17. The system as recited in claim 15 wherein saidreports include widths of said radar pulses and said report analyzeranalyzes widths of ones of said radar pulses.
 18. The system as recitedin claim 15 wherein said report analyzer identifies X successiverepetitions of a given time interval between ones of said radar pulsessubject to a maximum of Y missing radar pulses and within a tolerance ofZ microseconds, where X, Y and Z are programmable variables.
 19. Thesystem as recited in claim 15 wherein said report analyzer identifies amaximum of N time intervals between ones of said radar pulses, where Nis a programmable variable.
 20. The system as recited in claim 15wherein said wireless network conforms to IEEE 802.11a and said sequenceis associated with a radar operating in a 5 GHz band.